The present invention relates to a photosensitive material in which a radiation sensitive composition is encapsulated in a plurality of microcapsules and exposure of the composition controls the release of the internal phase from the microcapsules and the formation of an image. More particularly, the present invention relates to a photosensitive material of the aforementioned type wherein the internal phase released from the microcapsules in the image areas transparentizes an otherwise opaque image-receiving layer and images in the form of transparent windows in an opaque background are formed.
Photosensitive materials employing encapsulated radiation sensitive compositions are the subject of commonly assigned U.S. Pat. Nos. 4,399,209 and 4,440,846. In these applications, images are formed by reacting a color precursor with a color developer. The color precursor is typically encapsulated with a radiation sensitive composition such as a composition containing a polyethylenically unsaturated monomer. By image-wise exposing the material to actinic radiation and rupturing the microcapsules in contact with a developer sheet, the color precursor is only released in the areas in which images are formed and a dye image (the reaction product of the color precursor and the color developer) is obtained.
Other imaging systems employing photosensitive microcapsules include:
Berman, U.S. Pat. No. 3,219,446 discloses a transfer imaging process in which a blue-black dye is encapsulated with a photocrosslinkable polymer or a photopolymerizable monomer in a film or a layer of discrete microcapsules. In this system imaging is accomplished by image-wise exposing the layer of the encapsulated material to electromagnetic radiation to crosslink the polymer or polymerize the monomer. This is said to cause the liquid in the exposed microcapsules to assume a non-liquid, rigid condition, such that upon rupturing the microcapsules only the dye from the unexposed microcapsules is transferred to a receiving sheet where images are formed.
Phillips, U.S. Pat. No. 3,700,439, discloses a process wherein Michler's ketoneis encapsulated in a conventional manner and provided as a layer on a support. Michler's ketone is not a color former, but irradiation of the ketone converts it to a colorless, acid colorable, dye precursor. Thus, by image-wise exposing the Phillips material to actinic radiation and rupturing the microcapsules in contact with an acid developer layer, such as a layer of acid clay, a visible image is obtained in the areas in which the ketone has been converted to the acid colorable form by irradiation. Phillips also discloses a self-contained system in which the acid developer is on the same support as the microcapsules containing the Michler's ketone.
Levy, U.S. Pat. No. 4,149,887, relates to a microcapsule-containing imaging material having a photoconductive internal phase which is exposed in an RF field. Exposure increases the conductivity of the internal phase and causes the microcapsules to heat, swell and then rupture in the exposed areas thereby freeing the contents to form images. The microcapsules may contain color precursors which form images by reacting with a developing agent.
Japanese Kokai No. 6212/1974 to Matsushita Denki Sangyo K.K., relates to a recording material in which microcapsules having a photocrosslinkable polymer wall contain a colorless or substantially colorless precursor in a polar solvent and, optionally, an acid dye developer. The polar solvent prevents the color precursor from reacting with the acid dye developer and forming a color image. Images are formed by image-wise exposing the material to actinic radiation and rupturing the microcapsules in the unexposed areas, whereupon the polar solvent evaporates and color development occurs.
Japanese Kokai Nos. 9519 and 9520/1978 to K.K. Rikoh, relate to imaging systems in which the microcapsules contain a radiation curable internal phase including a dye precursor. Images are formed by image-wise exposing a layer of the microcapsules to light and selectively transferring the microcapsules from the unexposed areas to a receiving sheet. The microcapsules are not ruptured. Upon subsequent wet development processing of the transfer sheet with a dye developer, the dye precursor in the microcapsules is converted to a colored form and an image is obtained.
British Pat. Nos. 1,001,832; 1,058,798; 1,141,475; and 1,193,923 to DuPont relate to imaging materials which employ a photopolymerizable substratum comprising a solid binder having a polymerizable ethylenically unsaturated compound dispersed therein. Images are formed by image-wise exposing the materials to actinic radiation. Exposure controls the rate of diffusion of a developer into or out of the photopolymerizable substratum. In the case of '798, a dye or color precursor is present in the microcapsules and images are formed by bringing a receiving sheet, such as plain or coated paper, into contact with a substratum and heating the two in combination such that the dye diffuses from the unexposed areas of the substratum to the receiving sheet. In the case of '475, at least one of a color former, developer and oxidizing agent is present in the dispersed phase and the substratum is hardened in the exposed areas thereby altering the rate of diffusion of an externally applied reactant into the substratum.